1. Field of the Invention
The current invention relates to transport systems and methods for conveying articles along a conveyance path, and in some embodiments to conveying semiconductor wafers in a semiconductor fabrication facility.
2. Related Art
Transport systems are widely employed in industrial manufacturing facilities to convey articles between work stations. Originally, these systems were manual and workers moved articles by hand or by cart. Modern factories have developed specialized equipment to convey articles automatically. In particular, semiconductor fabrication facilities currently use automated transport systems to move semiconductor wafers during the manufacturing process. Typically, a batch of wafers may be conveyed together in a container known as a Front Opening Unified Pod (FOUP). Semiconductor wafer manufacturers have sought to increase manufacturing productivity by using transport systems that efficiently convey wafers from machine to machine without exposing the wafers to excessive contamination, vibration or to excessive acceleration and deceleration forces.
Existing transport systems employ vehicle-based devices to eliminate vibrations but the capacity of this system is limited by the number of vehicles available. To resolve this, transporters are used in which articles are, for example, directly conveyed across the horizontal surface of a transport belt on rollers, or directly on the rollers. One such transport system is shown in FIG. 1A. A common feature of these existing systems is the difficulty of vibrationally isolating the article being conveyed from the surface across which the articles travel. If the surface across which the articles travel is not flat, the articles experience vibration during the conveyance. This source of vibration is a known problem in the semiconductor wafer manufacturing industry. For example, as shown in FIG. 1A, Horizontal Rollers 110 include Circular Surfaces 120 on which a Horizontal Belt 130 rests. Horizontal Belt 130 may be characterized by a Length 140, a Long Cross-Sectional Axis 150, and a Short Cross-Sectional Axis 160. The Long Cross-Sectional Axis 150 and a Short Cross-Sectional Axis 160 are perpendicular to the length, and disposed in horizontal and vertical planes, respectively. The weight of a FOUP 170 is transferred through the Short Cross-Sectional Axis 160 of Horizontal Belt 130 onto Circular Surfaces 120, as is shown in FIG. 1B. Because Horizontal Belt 130 is flexible in the Short Cross-Sectional Axis 160 in which the weight of FOUP 170 is applied and is not continuously supported by Horizontal Rollers 110, the level of Horizontal Belt 130 varies between Horizontal Rollers 110. This unevenness limits the speed at which FOUP 170 can be conveyed while staying within vibration limits.
Another problem with existing transport systems used in the semiconductor wafer manufacturing industry is the difficulty of changing or turning the direction of conveyance of an article, such as a FOUP, without momentarily stopping its motion.
There are, therefore, needs for improved systems and methods for conveying articles in manufacturing facilities.